German Patent Application No. 1 96 42 343 has already describes a playback apparatus wherein a compact disc motor with an axle drives a recording carrier in the form of a compact disc secured between a first disc connected to the axle and a second disc.
The playback apparatus according to the present invention, has the advantage that a predetermined distance is provided between the storage disc and the first disc within a predetermined area, and the area and the distance are selected so that when there is vibration of the playback apparatus approximately normal to the plane of the disc with an acceleration not exceeding a predetermined value, there results an amplitude of a resulting vibration of an outside edge of the storage disc in relation to a mid point of the storage disc which is below a predetermined value. In this way, vibration of the storage disc can be dampened without requiring additional damping means due to the air layer between the storage disc and the first disc in the predetermined area and due to the change in volume between the storage disc and the first disc in the predetermined area, especially at the resonant frequency of the storage disc. Thus, when there is any vibration of the storage disc, the air layer between the storage disc and the first disc in the predetermined area and the change in volume between the storage disc and the first disc in the predetermined area function as damping means.
Another advantage is that when the storage disc experiences vibrations normal to the plane of the disc, position errors in focusing the tracks of an optical storage disc by means of a beam of light of a reading device for sampling the information stored in the tracks can be suppressed to a great extent, thus making the reading device highly resistant to vibration of the playback apparatus perpendicular to the plane of the disc. This is especially advantageous with a playback apparatus designed as a compact disc player where a disc drive is suspended without any additional damping means.
Another advantage is that the inertial forces transmitted to the housing of the playback apparatus with vibration of the playback apparatus are greatly reduced due to the damping of vibrations of the storage disc normal to the plane of the disc.
Another advantage is that the positioning force required to position the storage disc between the first and second discs, serving to position the storage disc on the second disc is reduced due to the damping of vibrations of the storage disc normal to the plane of the disc.
Due to the damping of the vibrations of the storage disc normal to the plane of the disc, the storage disc can thus be positioned with a lower positioning force with at the same time a reduction in its sensitivity to vibrations of the playback apparatus. When the second disc and with it the storage disc and the first disc are rotated by a motor-driven axle in operation for output of data, the motor and its bearings are less burdened by the positioning force for positioning the storage disc between the first disc and the second disc, thus lengthening its lifetime and maintaining the quality of the output for a long time.
It is especially advantageous that an essentially inelastic and porous material is arranged between the storage disc and the first disc in at least part of the predetermined area. This prevents scratching of a protective layer covering a metallized surface, for example, of the storage disc due to the storage disc repeatedly striking the first disc when the storage disc vibrates normal to the plane of the disc. Damping of the vibrations of the storage disc normal to the plane of the disc is possible due to the pores in the material, permitting a layer of air between the storage disc and the first disc. Damping of vibrations of the storage disc normal to the plane of the disc is further improved by using an inelastic material.